MLA

Wilder, Thornton, 1897-1975. Notes on South American Writers. Box 157, folder 3837. [1941?]. https://collections.library.yale.edu/catalog/17056690.

APA, 6th edition

Wilder, Thornton, 1897-1975. (["Box 157, folder 3837"])([1941?])[Notes on South American Writers]. https://collections.library.yale.edu/catalog/17056690.